The Wonderful Zenith K731

[ChiefRider]

My dad was a big Zenith fan- He bought a new T-O 1000 in '59, a Royal 50 in '61, and the Colonial style 731 around '63. When it was brand new, I remember he would listen to opera performances on the 731. I assumed posession of it when I entered high school, and had it on all the time. In fact, I remember listening to Howard Stern when he was an unknown local DJ in Hartford, CT. I still have this radio, but haven't used it in years. I figure the selenium rectifier should be replaced, and probably capacitors, too. I haven't done any electronics work in years, so I haven't dug into it. Seeing, this, I'd sure like to bring it back to daily use!

Chief

[Jeffhs]

Originally Posted by ChiefRider

My dad was a big Zenith fan- He bought a new T-O 1000 in '59, a Royal 50 in '61, and the Colonial style 731 around '63. When it was brand new, I remember he would listen to opera performances on the 731. I assumed posession of it when I entered high school, and had it on all the time. In fact, I remember listening to Howard Stern when he was an unknown local DJ in Hartford, CT. I still have this radio, but haven't used it in years. I figure the selenium rectifier should be replaced, and probably capacitors, too. I haven't done any electronics work in years, so I haven't dug into it. Seeing, this, I'd sure like to bring it back to daily use!

Chief

Any antique or vintage radio should be recapped as a matter of routine, as capacitors deteriorate over time. The three-section electrolytic in the power supply in particular probably should be replaced if the radio still has the original, even if the radio exhibits no hum or other problems. These electrolytics can short without warning; when they do short, the radio will blow the house fuses as soon as it is plugged in (doesn't have to be on) because the filters are in a position to short the power line directly to ground when they go bad (short). Dried-out electrolytics will produce a loud 60-Hz hum in the speaker; the radio may still work until the capacitor eventually shorts, but the sound will be terribly distorted.

As to the selenium rectifier, this can and should be replaced with a silicon diode as soon as possible. Seleniums will give off a gas that smells of rotten eggs when they short, so you will know when it goes! (This gas is toxic as well.) The job is not difficult and shouldn't take more than a few minutes; however, a dropping resistor must be used in series with the diode so that the output voltage will match that of the original selenium stack.